Fuel Composition

ABSTRACT

A fuel composition includes a lower alkyl monool(s) and C 2 -C 6  esters of one or more long chain fatty acids. Generally, C, H and O atoms constitute at least 99.99% (by wt.) of the composition, and the composition can be essentially free of sulfur and/or nitrogen atoms. The composition can be provided by adjusting to less than 7.0 the pH of a liquid that contains at least one C 2 -C 6  ester of one or more long chain fatty acids. The C 2 -C 6  ester(s) can be provided by transesterifi-cation of a triglyceride-containing composition using a C 2 -C 6  monool, which preferably is present in stoichiometric excess.

BACKGROUND INFORMATION

Diesel engines continue to find wide use in trucks, ships, trains, and the like. Commercially acceptable diesel fuel must be capable of performing over a range of climatic conditions and, accordingly, must be able to be used at temperatures down to 0° C. and preferably as low as at least −10° C.

Diesel engine exhaust often includes particulates, CO, and various nitrogen oxide (NO_(x)) species. Over the years, many attempts to address the environmental concerns associated with exhaust fumes from diesel engines have focused on lower alcohols such as methanol and ethanol. A blend of 15% (by vol.) ethanol and 85% (by vol.) diesel oil has been found to improve the combustion byproducts emitted in the engine exhaust (generally believed to be due to the increased oxygen content of the fuel) without requiring modifications to existing diesel engines; in recent years, the amount of ethanol has been increased at times to 20% (by vol.). However, lower alcohols typically are immiscible with diesel oil and tend to separate over time, so the components often are stored separately and mixed just prior to use.

Fuel blends of the type just described often are referred to as “E-diesel” (or some similar variant). Although E-diesel typically generate fewer objectionable combustion byproducts than neat diesel oil, it produces less energy when combusted and still employs petroleum-derived diesel oil for at least 80% of its volume. Sustainability and sourcing concerns regarding fossil fuels have grown significantly over the past decade. In turn, this has increased interest in fuels prepared from sources other than petroleum has grown significantly over the past decade or so.

Much of this interest has focused on so-called biofuels, which are the transesterification products of any of a variety of animal fats and vegetable oils. The major components of oils and fats are fatty acid triglycerides, molecules in which three long chain fatty acids are ester linked to a glycerol radical. When the oil or fat is exposed to an alcohol (typically methanol) under appropriate catalytic conditions, the fatty acids can cleave from the glycerol radical and react with the alcohol to form fatty acid esters. The transesterification reaction significantly reduces the viscosity of the oil.

The triglyceride transesterification reaction has been much studied; for more information on the manufacture and properties of such biofuels, the interested reader is directed to any of a variety of overviews such as, e.g., M. Graboski et al., “Combustion of Fat and Vegetable Oil Derived Fuels in Diesel Engines,” Prog. Energy Combust. Sci., vol. 24, pp. 125-64 (1998, Elsevier).

Biofuels can be used neat but, more commonly, small proportions are blended into petroleum-derived diesel (hereinafter “petrodiesel”). Blends of biofuel and petrodiesel often are referred to as B-diesel or, more commonly, with a number following the B to indicate the percentage of petrodiesel replaced with biodiesel (e.g., B20 diesel indicating of blend of 80% petrodiesel and 20% biodiesel).

Some have attempted to combine alcohol and biofuel in a single composition; see, e.g., U.S. Pat. No. 6,129,773 and U.S. Patent Appl. Publ. No. US 2003/0126790 A1.

Fuel compositions that include components derived solely from renewable starting materials appear to be of continued and growing interest. Ideally, such a biofuel composition could be used in essentially the same climatic conditions as, and have emission characteristics that are better than, petrodiesel. Additionally, such compositions also preferably would produce nearly as much energy as an equivalent volume of petrodiesel while resulting in similar or better engine wear characteristics.

SUMMARY

In one aspect is provided a fuel composition that includes ethanol and a C₂-C₆ ester of one or more long chain fatty acids. The composition generally includes at least about 2.5% (by vol.), typically from about 5 to about 10% (by vol.), of a lower alkyl monool such as ethanol and a complementary amount of long chain fatty acid ester(s); all other components typically are present in no more than trace amounts.

In some embodiments, at least 99.99% (by wt.) or even 99.999% (by wt.) of the composition can constitute just C, H and O atoms; in these and other embodiments, the composition can be essentially free of at least one of, and preferably both of, sulfur and nitrogen atoms.

The composition typically includes at least about 0.2% (by vol.), commonly at least about 0.25% (by vol.), and occasionally at least about 0.3% (by vol.) water. In some embodiments, the fuel composition can include at least about 0.5% (by vol.) water. Water in a fuel composition typically is considered something to be avoided if at all possible, yet the presence of up to about 1% (by vol.) has not proven to be particularly deleterious to the efficacy of the present fuel composition.

In some embodiments, the fuel composition can have an acidic pH, at times as low as, e.g., 4.5, but more commonly from about 6.0 to about 6.8.

The composition typically has a kinematic viscosity of from about 3.5 to about 4.0 mm²/s (i.e., cSt), commonly about 3.7±0.2 mm²/s. Even in the absence of flow improving additives, the composition can have a cloud point of at least as low as about −5° C. and a pour point of at least as low as about −15° C.

In another aspect is provided a method for synthesizing and refining a fuel composition. The method includes providing a liquid that contains at least one C₂-C₆ ester of one or more long chain fatty acids and adjusting the pH of the liquid to less than 7.0. The C₂-C₆ ester(s) can be provided by transesterification of a triglyceride-containing composition using a C₂-C₆ monool and, in such cases, the pH adjustment results in separation of a salt and glycerine-related byproducts (e.g., glycerol) from the liquid phase, thereby resulting in a raw fuel composition. The raw fuel composition then is treated so as to remove particulates having an average diameter greater than ˜1 μm and to ensure that the concentration of Group I metal ions is less than about 50 parts per million (ppm), preferably even 5-10 times lower than this number.

The transesterification process typically is performed in the presence of a stoichiometric excess of one or more C₂-C₆ alcohols. The alcohol(s) typically are present in from ˜25 to ˜200% excess (by vol.), preferably from ˜50 to ˜150% excess, more preferably from ˜70 to ˜130% excess, and most preferably from ˜80 to ˜120% excess.

The pH of the liquid, as well as the raw fuel composition and the fuel composition that ultimately results from the refining process (at least initially), typically is between about 4.5 and about 6.8, preferably of from about 5.0 to about 6.75, more preferably of from about 5.5 to about 6.7, and most preferably from about 6.0 to about 6.65. Refining the fuel composition in a slightly acidic condition can provide storage stability benefits.

In certain embodiments, the pH adjustments is accomplished by adding a strong acid to the liquid. In some of these embodiments, the acid is halogenated (e.g., HCl), and the salt removed from the liquid is KX where X is a halogen atom (e.g., Cl).

In some embodiments, the raw fuel treatment can be accomplished by passing the raw fuel composition through a series of filters, optionally of progressively smaller pore sizes.

The process can provide a fuel composition that has a kinematic viscosity of from about 3.5 to about 4.0 mm²/s, most commonly of no more than about 3.8 mm²/s.

The process also can provide a fuel composition that remains fluid even in the absence of flow improving additives. Specifically, the composition can have a cloud point at least as low as −5° C. and a pour point at least as low as −15° C. The cetane number of a refined fuel composition typically is greater than about 45 and can be significantly (e.g., 5-15%) higher.

Advantageously, all steps of this process can be performed without utilizing external sources of heat, i.e., at or near ambient temperatures. Additionally, the process can be performed without the addition of significant amounts of water, thereby eliminating the need to collect and treat (typically very caustic) waste water.

In yet another aspect is provided a method of powering a vehicle. The method involves introducing a fuel that includes the aforesaid fuel composition into a diesel engine and allowing the engine to combust the fuel. Advantageously, the aforesaid fuel composition can result in simultaneous reductions in opacity, CO, SO₂, and NO_(x) in the exhaust compared to the exhaust of the same engine combusting petrodiesel. Simultaneously, the amount of O₂ in the same exhaust increases relative to that seen when petrodiesel is combusted. In many cases, the aforesaid composition also greatly reduces the amount of and, in some instances, removes carbonaceous deposits (often referred to as “coking”) on metal parts of the engine. With the probable exception of the detergency effect and lower exhaust temperatures, the other characteristics might be more evident in a two-cycle diesel engine than in a four-stroke diesel engine.

Other aspects of the invention are set forth in the more detailed description which follows.

DETAILED DESCRIPTION

The process of making a fuel composition, more specifically a process that involves synthesizing and refining a fuel composition, is described first.

Like other biofuel manufacturing processes, the synthesis portion of the process involves a transesterification reaction. However, certain aspects of the reaction differ from that which has become conventional in the manufacture of biofuels.

Almost any triglyceride can be transesterified with an alcohol. For example, as described above, some are using the filtered waste oil from fast food restaurants as a low-cost reactant. However, the present process gives preference to highly pure vegetable oils, more preferably to food-grade materials, examples of which include corn, linseed, peanut and soybean oils.

For the convenience of the reader, the following tables provide approximate percentages of various saturated and unsaturated fatty acid components of a variety of fats and oils. The first is from page 130 of the aforementioned Graboski et al. article, while the second is from Appendix A of C. L. Peterson et al., “Performance and Durability Testing of Diesel Engines Using Ethyl and Methyl Ester Fuels,” Nat'l Biodiesel Bd. Report for 1995, received for publication on Feb. 27, 1996. The former provides data for raw materials (i.e., ones that have not undergone transesterification), while the latter provides data for esterified fatty acids in biofuels made from such materials.

TABLE 1a Weight percentages of fatty acids in fats and oils Carbon number Saturated acids Mono-unsaturated acids 8 10 12 14 16 18 >18 <16 16 18 >18 Di Tri Beef tallow — — 0.2 2-3 25-30 21-26 0.4-1   0.5 2-3 39-42 0.3 2  — Butter 1-2 2-3 1-4  8-13 25-32  8-13 0.4-2   1-2 2-5 22-29 0.2-1.5 3  — Coconut 5-9  4-10 44-51 13-18  7-10 1-4 — — — 5-8 — 1-3 — Cod liver — — — 2-6  7-14 0-1 — 0-2 10-20 25-31 35-52 — — Corn — — — 0-2  8-10 1-4 — — 1-2 30-50 0-2 34-56 — Cottonseed — — — 0-3 17-23 1-3 — — — 23-41 2-3 34-55 — Lard — — — 1   25-30 12-16 — 0.2 2-5  4-51 2-3  4-22 — Linseed — — — 0.2 5-9 0-1 — — —  9-29 —  8-29 45-67 Palm — — — 1-6 32-47 1-6 — — — 40-52 —  2-11 — Palm kernel 2-4 3-7 45-52 14-19 6-9 1-3 1-2  — 0-1 10-18 — 1-2 — Peanut — — — 0.5  6-11 3-6 5-10 — 1-2 39-66 — 17-38 — Rapeseed — — — — 2-5 1-2 0.9 — 0.2 10-15 50-60 10-20  5-10 Safflower — — — — 5.2 2.2 — — — 76.3 — 16.2 — Soybean — — — 0.3  7-11 3-6 5-10 — 0-1 22-34 — 50-60  2-10 Sunflower — — — — 6   4.2 1.4 — — 18.7 — 69.3 0.3 Tung — — — — — — — — —  4-13 —  8-15 72-88

TABLE 1b Weight percentages of fatty acids in fats and oils Carbon number Mono-unsaturated Saturated acids acids 14 16 18 >18 18 20 22 Di Tri Beef 3 23-24 18 0   38-39 0   0  0 0 tallow Canola 0  4 2-3 0.5 65 1-2 0.1-0.2 17-18 7-8 Rape- 0 2-3  1 0.5-1   12-13 7-8 49-50 12 7-8 seed Soy- 0 10 3-4 0-0.5 19 0.2 0 55-56 10-11 bean (The numbers in Table 1b do not add to 100% in all cases because some materials contained other, non-analyzed constituent fatty acids.)

A preferred starting material is a food-grade vegetable oil selected from the foregoing list. Particularly preferred are those that are refined, bleached, and deodorized (RBD); such materials are available from a variety of commercial sources including, for example, ConAgra, Bunge Ltd., ADM and the like. The remainder of this description is based on an RBD soybean oil although, in view of the advantages found with this material and its composition relative to that of other oils, the ordinarily skilled artisan should be able to identify other sources of long chain fatty acids that can provide similar advantages and/or advantages in different end-use conditions.

The fatty acid source(s) can be provided in or to a reaction vessel. While the art teaches that most any type of vessel can be used, preparation of a high quality biodiesel-type fuel composition is facilitated by use of a vessel made from a clean, essentially non-reactive material. Preference here is given to materials such as steel, stainless steel, glass-lined metals, and the like.

The other reagent in transesterification reactions is an alcohol. The vast majority of biofuels being made employ methanol as a reagent. In fact, the European Biodiesel Board mandates the use of methanol where a producer wishes to have its product certified as a biodiesel fuel; see, e.g., EN14214. However, distinct advantages have been found when higher alcohols, specifically one or more C₂-C₆ alcohols, are employed. Non-limiting examples of these benefits include improved miscibility with petrodiesel and better low temperature performance as exemplified by, e.g., cloud point and cold pour point.

Each alcohol employed preferably is aliphatic, and more preferably has the general formula C_(n)H_(2n+1)OH where 2≦n≦6. As indicated by the formula, the use of monools is preferred so as to avoid the formation of longer chain diesters. Preferred alcohols include ethanol, 1-propanol, 2-propanol, and 1-butanol, with absolute ethanol (denatured by means of, e.g., gasoline) being particularly preferred.

Where the emission characteristics of the resulting fuel are of concern, the alcohol preferably is free of heteroatoms that can be involved in the formation of undesirable species; non-limiting examples of such heteroatoms include N, S, and P.

Reaction between the alcohol(s) and triglyceride(s) is catalyzed by both acids and bases, with a strong base being more commonly used. Typically, no more than ˜1% (by wt.) catalyst is required, based on the triglyceride starting material(s).

Conveniently, the catalyst can be delivered in some or all of the alcohol(s). This can be done by dissolving a strong base, e.g., KOH, in the alcohol(s) prior to delivery of the alcohol(s) to the reaction vessel. Conveniently, this can be done in a relatively short amount of time (less than an hour) through simple mixing at ambient or slightly elevated temperatures. If desired, the catalyst solution can be added stepwise, i.e., through the addition of sequential aliquots followed by mixing or agitation.

An excess of alcohol preferably is introduced to the reaction vessel. As noted previously, the fuel composition contains both C₂-C₆ esters of long chain fatty acid(s) and C₂-C₆ alcohol(s). Rather than delivering a stoichiometric amount of alcohol to the reaction vessel and then later blending the resulting transesterified product(s) with additional alcohol, certain processing and performance advantages might be obtained by introducing the alcohol component(s) during the transesterification step. In practice, a significant excess of alcohol can be added to the reaction vessel; the amount typically ranges from ˜25 to ˜200%, preferably from ˜50 to ˜150%, more preferably from ˜70 to ˜130%, even more preferably from ˜80 to ˜120%, and most preferably at least ˜100% excess (all by volume).

Despite the aforementioned preference for using an excess of alcohol during the manufacture and refining steps, at least some of the benefits might be able to be achieved by post-manufacture addition of alcohol during or after refining.

To a certain extent, the stoichiometric excess of alcohol can be varied somewhat so as to create fuel compositions with slightly different properties. In this manner, one can create seasonal blends of fuel. For example, during cold weather seasons, the excess of alcohol can be increased so as to provide a fuel composition having a lower viscosity than a similar composition intended for summertime use.

The process has been described as involving introduction of the basic alcohol solution to the oil, although this is not to be considered limiting. Where this is done, however, introducing the alcohol solution near the bottom of the tank and allowing it to partition upwardly can provide some reaction advantages, particularly where the reaction mixture is not agitated, stirred, etc., and where the transesterification reaction is permitted to proceed at or near ambient temperatures. Where conventional agitation techniques (e.g., a circulating pump) are employed, the transesterification reaction generally proceeds to completion in a few hours at 20°-25° C. The transesterification reaction can be expedited with relatively gentle heating although this certainly is not required.

The second product of the transesterification reaction is glycerol and other glycerine byproducts. Depending on the identity, nature, and purity of the reagents, the glycerol in the reaction vessel can separate on its own, can partially separate, or separate only minimally. For example, where high purity reagents are used, glycerol (and derivatives) typically separates from the alkyl ester/ethanol phase in a few hours (e.g., 4-12 hours) after agitation is ceased. However, where a less refined starting material is employed, addition of more alcohol (e.g., up to ˜20% additional alcohol) and/or additional time can be needed to achieve the desired level of separation. The alcohol added for separation purposes need not be the same as that used in the reaction and, in fact, methanol can be used for this purpose, if desired.

The glycerol phase is heavier than the alkyl ester/alcohol phase and thus separates to the bottom of the reaction vessel. Where the reaction vessel includes an egress at or near its bottom, the glycerol layer can be drained from the reaction vessel. Typically, the glycerol phase constitutes from ˜10-20% of the triglyceride reactant. Based on the excess amount of alcohol used during the transesterification reaction, the glycerol layer is presumed to contain a not insignificant amount of alcohol. Processing and/or disposal techniques for glycerol are known.

Assuming that the material used as the basic catalyst contains a Group I or II metal atom (e.g., KOH or Ca(OH)₂), the majority of the Group I or II metal ions partition into the glycerol phase. Removing the glycerol phase thereby conveniently removes the majority of Group I or II metal ions present in the reaction vessel. The remaining alkyl ester/alcohol phase typically contains on the order of 500 to 1000 ppm of such ions, more commonly on the order of 600 to 800 ppm.

The alkyl ester/alcohol blend can be further treated in the reaction vessel or, more commonly, transferred to one or more additional vessels for further refining. At this point, the blend typically has a kinematic viscosity of ˜6.2 to ˜6.8 mm²/s.

Organizations such as the National Biodiesel Board (NBB) suggest techniques in which the raw fuel (which, assuming stoichiometric amounts of triglyceride and methanol, will be extremely caustic) is washed repeatedly with water. This repeated washing uses large amounts of another natural resource (i.e., water) and results in huge volumes of moderately to extremely caustic waste water which, in turn, must be treated before and/or after disposal.

Conversely, the present process gives preference to techniques that do not employ water per se. For example, the raw fuel composition can be passed by or through a cationic exchange resin which replaces Group I or II metal ions with H atoms. Such resins are widely known and available from a variety of commercial sources including, e.g., Rohm and Haas Co. (Philadelphia, Pa.).

Alternatively, relatively small amounts of a strong acid can be used to neutralize the alkyl ester/alcohol blend. Halogen-containing strong acids (e.g., concentrated HCl) are preferred over other strong acids that contain the types of heteroatoms mentioned previously, e.g., H₂SO₄, HNO₃, etc. While the ordinarily skilled artisan can perform the stoichiometric calculations needed to determine the amount of a given acid needed to neutralize a given raw fuel composition, by way of non-limiting example, each liter of concentrated HCl can treat over 500 L of raw fuel composition.

Such refining techniques result in removal of Group I or II metal ions. Where acid is added to the blend, the ions are removed as salt along with a very significant portion of any glycerol-type byproduct that did not phase separate previously. The latter is evidenced by a fairly significant reduction in kinematic viscosity. As mentioned previously, a raw fuel composition typically has a kinematic viscosity at 40° C. of ˜6.5 mm²/s; conversely, the same composition having undergone the type of acidulation refining just described typically has a kinematic viscosity at 40° C. of from ˜4.0 to ˜5.5 mm²/s. This is believed to be somewhat better than that which can be attained through simple water washing and/or use of ion exchange resins. For example, in the aforementioned Peterson et al. article, the various ethyl ester biofuels had kinematic viscosities of from 4.5 mm²/s (soybean oil) to 6.2 mm²/s (rapeseed oil).

Regardless of which refining technique is used, the processed fuel composition (i.e., purified alkyl ester/alcohol blend) preferably is rendered very slightly acidic, whereas generally accepted techniques which argue for a refined fuel that is essentially neutral (pH=7.0). At this point in the refining process, the alkyl ester/alcohol blend can register a pH of as low as 4.0 to 4.5, typically between about 4.5 and about 6.9; more commonly, the pH of the blend will be in one or more of the following ranges: about 5.0 to about 6.8, about 5.5 to about 6.75, about 5.75 to about 6.7, about 5.9 to about 6.7, about 6.0 to about 6.75, about 6.0 to about 6.7, about 6.1 to about 6.6, about 6.1 to about 6.7, and about 6.4±0.2.

(For fuel compositions, particularly biofuels, acid numbers commonly are reported. This is a measure of free, i.e., non-esterified fatty acids and is given in terms of mg KOH necessary to neutralize those fatty acids. When a strong protic acid is utilized in the refining of the present fuel composition, this acid number is believed to be far less meaningful. For at least this reason, a conventional pH meter was employed to obtain pH measurements, and these are the numbers used herein.)

By providing a fuel composition with a slightly acidic pH, storage and handling advantages have been observed without any noticeable deleterious effects on performance. Specifically, fuel compositions refined so as to have an essentially neutral pH at this step have been observed to form a flocculent or precipitate when stored for extended periods and/or, particularly, when exposed to air. Conversely, fuel compositions with a slightly acidic pH have not been observed to suffer from this tendency.

At this point of the refining process, the fuel composition includes primarily alkyl esters of long chain fatty acids and alcohol; most other materials are present in essentially just trace amounts. However, the fuel composition generally includes from about 0.2 to about 0.9% (by vol.), commonly from about 0.25 to about 0.75% (by vol.), and at times from about 0.3 to about 0.6% (by vol.) water. This amount of entrained or dispersed water is not significantly reduced even when the fuel composition is filtered, as discussed in more detail below; nevertheless, the presence of such water has not been found to have significant deleterious effects on combustion of the fuel composition and might even provide certain benefits (e.g., reduced combustion temperatures).

Additionally, at this stage of the refining process, the amount of Group I or II metal ions typically is reduced to no more than about 50 ppm, preferably no more than about 25 ppm, more preferably no more than about 10 ppm, even more preferably no more than about 5 ppm, and most preferably no more than about 4 ppm.

The fuel composition can include up to about 50% (by vol.) alcohol relative to the overall volume. The fuel composition generally can include from about 2 to about 40% (by vol.) alcohol, although from about 3 to about 30% (by vol.) is more common and from about 4 to about 20% (by vol.) is most common. Where high purity reagents are employed (as described above), a refined fuel composition made according to this process typically includes from ˜5 to ˜15% (by vol.), commonly from ˜5.5 to ˜10% (by vol.), and most commonly from ˜6 to ˜8% (by vol.) alcohol; preferably one or more C₂-C₄ monools such as ethanol and/or 1-butanol.

At this point, several options are available. For example, the refined blend can be used as is or can be used after addition and thorough mixing of one or more conditioners, stabilizers, or other additives (e.g., kerosene). However, certain further advantages can be obtained by additional refining of the fuel composition, optionally containing additives of the types of just discussed.

An additional refining technique that has been found advantageous in certain circumstances is filtering. Specifically, the fuel composition can be passed through one or more filters, optionally of progressively smaller pore size, so as to remove suspended contaminants. Commercial filtration devices are available from a variety of sources including, e.g., Donaldson Co., Inc. (Minneapolis, Minn.), Central Illinois Manufacturing Co. (Bement, Ill.), Harvard Corporation (Evansville, Wis.), and Wix Filtration Products (Gastonia, N.C.). Using a pump to pressurize the system to ˜130 to ˜140 kPa can provide a processing rate on the order of ˜550 to ˜700 mL/s.

Performing such filtration on raw fuel compositions has not been found to provide significant advantages, at least on a consistent basis. However, when filtration is done on a fuel composition that has been treated by the aforementioned acidulation technique, fuel compositions having kinematic viscosities at 40° C. on the order of no more than ˜4.2 mm²/s, of no more than ˜4.1 mm²/s, of no more than ˜4.0 mm²/s, of no more than ˜3.9 mm²/s, of no more than ˜3.8 mm²/s, and even of no more than ˜3.7 mm²/s can be obtained. This technique is believed to be capable of providing an ethyl ester of soy oil/ethanol fuel composition with a kinematic viscosity at 40° C. on the order of ˜3.6 mm²/s, ˜3.5 mm²/s, or even lower. These viscosity values are in contrast to those reported for prior art ethyl ester biofuels; see, e.g., the Peterson et al. article data mentioned above as well as the Graboski et al. article (from 4.4 to 5.9 mm²/s). Additionally, the presence of free alcohol(s) in the fuel composition can explain no more than about half of the viscosity reduction seen in the present fuel composition. An explanation for the remainder of this reduction is not fully understood but might result from the acidulation step making one or more of the undesired byproducts more susceptible to removal by further refining steps such as, e.g., filtration.

Thus, a fuel composition that has been both acidulated and filtered can have a kinematic viscosity that is on the order of 40% less than that of the raw fuel from which it has been refined. Because petrodiesel generally is expected to have a kinematic viscosity of no more than 4.1 mm²/s when measured at 40° C. in accordance with ASTM D975, providing a biofuel with similar viscosity characteristics can be advantageous with respect to both commercial acceptance and in-use performance. The ordinarily skilled artisan understands the desirability of having a biofuel composition that has storage and performance characteristics that are as similar as possible to ubiquitous petrodiesel. For example, published reports including the aforementioned Peterson et al. article indicate that coking of fuel injectors might correlate directly to fuel viscosity. Coking also has been surmised to be due to impurities in the biofuel; see again, e.g., the Peterson et al. article. These two theories might be related: refining that leads to fewer impurities likewise might result in a reduction in viscosity.

The refining process just described is believed to provide significant benefits over those commonly employed in the manufacture of biodiesel fuel. For example, this process does not require the use of large volumes of water to wash Group I ions out of the raw fuel composition; in turn, this reduces the amount of water that must be used and treated prior to disposal. Additionally, because excess alcohol in the refined fuel composition is desirable, this process does not require the use of time- and energy-intensive distillation techniques. Thus, in addition to using essentially only natural starting materials, the process requires the input of very little energy to make and refine a fuel composition.

Once fully refined, the fuel composition can be stored without a need for significant treatments or precautions. As mentioned previously, by refining the fuel composition in a slightly acidic form, better storage and handling performance can be achieved. However, whether the fuel composition must be maintained in acidic form once refining is completed has not been determined. In other words, the pH of the refined fuel composition might be able to be adjusted upwardly so that fuel composition has an essentially neutral pH prior to use without negatively affecting the viscosity and storage stability of the fuel composition once the refining process is complete.

Advantageously, this process can result in a fuel composition having a cloud point (as measured in accordance with ASTM D2500) of at least as low as about −2° C., −3° C., −4° C., −5° C., −6° C., −7° C., or even lower, and a pour point (as measured in accordance with ASTM D97) of at least as low as −10° C., −12.5° C., −15° C., −17.5° C., −20° C., or even lower. For example, a fuel composition made from ethanol and RBD soybean oil according to the foregoing process, treated with a small amount of diesel conditioner, was found to be in useful condition even after sitting outside overnight in air temperatures that fell to at least −20° C.; commercially available biodiesel fuels, even those with significant amounts of conditioners and other additives, are not believed capable of achieving this type of low temperature performance. For example, the Peterson et al. article reports that ethyl esters of fatty acids have pour points of from −10° (ethyl ester of rapeseed oil) to 12° C. (ethyl ester of beef tallow). By way of a more direct comparison, that same article indicates that an ethyl ester of soybean oil has a pour point of −3° C.; accordingly, the present process appears to be capable of providing fuel compositions with pour points that are at least 5° to 20° C. lower than those of standard ethyl ester biofuels.

A fully refined fuel composition can be used as is or, depending on the end use application, diluted with an appropriate amount of petrodiesel. For example, some fueling locations have created a 50:50 blend of bio- and petrodiesel and then used this blend as a masterbatch for providing further diluted blends. To date, no significant miscibility issues have been reported, even with the so-called masterbatch blends.

As suggested previously, a fuel composition according to the present invention generally includes a lower alkyl monool (e.g., ethanol) and a C₂-C₆ ester of one or more long chain fatty acids. The composition generally includes from about 5 to about 10% C₂-C₄ alcohol(s), preferably ethanol, and a complementary amount of long chain fatty acid ester(s); all other components typically are present in no more than trace amounts. In some embodiments, at least 99.99% (by wt.) or even 99.999% (by wt.) of the composition can constitute just C, H and O atoms; in these and other embodiments, the composition can be essentially free of at least one of, and preferably both of, sulfur and nitrogen atoms.

The composition generally includes water, typically in an amount of from about 0.2 to about 0.5% (by vol.) and amounts of as much as 0.8% (by vol.) or more are believed possible in certain circumstances.

For reasons already discussed, the fuel composition preferably has a slightly acidic pH (at least during refining) and a kinematic viscosity at 40° C. of about 3.7±0.2 mm²/s. Even in the absence of flow improving additives, the composition can have a cloud point of at least as low as about −5° C. and a pour point of at least as low as −15° C. Each of these properties can be achieved in isolation or, in some embodiments, in combination.

A biofuel composition of this type can be used neat and, in some circumstances, can provide significant emission advantages over neat petrodiesel or a blend of petrodiesel and biofuel.

For example, a fuel composition including ethanol and an ethyl ester transesterification product of RBD soybean oil was tested in a short rail line locomotive (EMD model 16-645BC) employing a two-cycle, V-16, roots blown, non-turbocharged engine; each cylinder had a displacement of ˜10.5 L (645 cubic inches), resulting in a total displacement of nearly 170 L. Prior to testing, the locomotive was provided with ˜280 L (75 gallons) of neat biofuel composition and allowed to warm up, thereby flushing any remaining petrodiesel from the engine. Thereafter, ˜190 L (50 gallons) of each of the following fuels were tested sequentially: neat biofuel, a 50:50 blend of biofuel composition and railroad off-road #2 petrodiesel, and neat petrodiesel. Emissions testing was performed with the engine under a steady state load created by connecting the locomotive's diesel powered DC generator to a loading grid designed to convert electrical power to heat.

Percent smoke opacity was measured continuously using a Wager™ 7500 smoke meter (Robert H. Wager Co., Inc.; Rural Hall, N.C.) clamped on a 5 cm (2 inch) sampling elbow tube placed inside one of the exhaust stacks of the locomotive.

Emission gases were measured using a Testo™ 350XL portable gas analyzer (testo, Inc.; Flanders, N.J.) set to measure exhaust O₂, CO, SO₂, total hydrocarbons, NO, NO₂, and combined NOx levels. (Total hydrocarbon data was not collected due to a sampling issue.) The analyzer came equipped with a model 450 control unit and attached sampling probe. The gas analyzer probe was maintained in a constant sampling position by a bracket that held the probe approximately 5 cm (2 inch) into the center of the exhaust stack.

Data collection began once the opacity readings stabilized after introduction of each test fuel. After this initial recording, readings were continuously charted in 1-2 minute intervals.

The results of this testing summarized below in Table 2 are averages of five of these values.

TABLE 2 Exhaust Characteristics, Two-Cycle Diesel Engine 100% petrodiesel 50:50 blend 100% biodiesel Temp. (° C.) 419 404 370 Opacity (%) 15 4 2 [SO₂] (ppm) 89 28 0 [O₂] (vol. %) 12.7 13.2 13.9 [CO] (ppm) 257 120 60 [NO_(x)] (ppm) 1225 1114 1047

The data from Table 2 indicate many interesting characteristics. For example, because the fuel composition according to the present invention was synthesized and refined in a manner that avoided the introduction of S atoms, the 100% reduction relative to #2 diesel oil (petrodiesel) might be explainable, although it still is better than results reported previously (e.g., the Peterson et al. article). Additionally, because the inventive fuel composition resulted in a lower exhaust temperature, the reduction in NO_(x) emissions also might be readily explainable (because NO_(x) formation is known to increase as combustion temperatures increase). Further, the higher oxygen content of the inventive fuel composition simultaneously increased the O₂ content and greatly reduced (i.e., more than 75%) the CO concentration of the exhaust.

The foregoing results contrast with those of a previously published study comparing off-road #2 petrodiesel (one meeting current EPA regulations and another meeting stricter California regulatory standards) with B20 diesel, i.e., an 80:20 blend of petrodiesel and a methyl ester derivative of soybean oil. See S. G. Fritz, “Evaluation of Biodiesel Fuel in an EMD GP38-2 Locomotive,” National Renewable Energy Laboratory Subcontractor Report dated May 2004 (available from the U.S. Dept. of Commerce).

That study was performed on a road-switcher locomotive equipped with an EMD 16-645-E diesel engine having the characteristics set forth below in Table 3.

TABLE 3 Specifications, Engine Used in Comparative Test engine type 2-stroke, uniflow scavenged diesel aspiration roots blown, non-turbocharged bore (mm) 230 stroke (mm) 254 number of cylinders 16 displacement (L), each cylinder 10.6 total displacement (L) 169 compression ratio 16:1 rated power (kW) 1491 rated speed (rpm) 900

The results from that exhaust emissions study are provided below in Tables 4a and 4b, where EPA-1 through EPA-3 are three tests performed on a diesel fuel meeting the U.S. Environmental Protection Agency specifications for locomotive emissions (see 40 C.F.R. §92.113); Cal-1 through Cal-3 are three tests performed on a 50:50 blend of two commercially available fuels meeting California Air Resources Board specifications; B20-1 through B20-3 are three tests performed on a 20:80 blend of G-3000™ biofuel (Griffin Industries, Inc.; Cold Spring, Ky.) and the fuel used in the EPA-1 through EPA-3 tests; C20-1 through C20-3 are three tests performed on a 20:80 blend of G-3000™ biofuel and the fuel used in the Cal-1 through Cal-3 tests; CBSFC is the Association of American Railroads-corrected brake-specific fuel consumption; and c.o.v. is the coefficient of variation of the three tests.

TABLE 4a Results from Comparative Emissions Testing, EPA Line-Haul Duty Cycle total hydrocarbons CO NO_(x) particulate matter CBSFC (g/hp · hr) (g/hp · hr) (g/hp · hr) (g/hp · hr) (lb/hp · hr) EPA-1 0.71 5.9 11.9 0.47 0.433 EPA-2 0.62 5.1 12.3 0.49 0.435 EPA-3 0.58 5.1 12.9 0.44 0.434 Mean 0.64 5.4 12.4 0.46 0.434 c.o.v. 10%   9% 4% 5% 0% Cal-1 0.63 4.6 12.2 0.48 0.431 Cal-2 0.62 4.7 12.0 0.46 0.429 Cal-3 0.67 3.7 12.6 0.45 0.433 Mean 0.64 4.3 12.3 0.46 0.431 c.o.v. 4% 13% 3% 4% 0% B20-1 0.66 5.3 12.6 0.48 0.430 B20-2 0.63 4.2 13.0 0.55 0.431 B20-3 0.64 3.9 13.6 0.46 0.434 Mean 0.64 4.5 13.1 0.50 0.432 c.o.v. 2% 17% 3% 10%  0% C20-1 0.63 4.2 12.9 0.49 0.434 C20-2 0.63 3.9 12.8 0.48 0.431 C20-3 0.67 3.9 12.8 0.48 0.432 Mean 0.64 4.0 12.8 0.48 0.432 c.o.v. 4%  4% 1% 2% 0%

TABLE 4b Results from Comparative Emissions Testing, EPA Switch Duty Cycle total hydrocarbons CO NO_(x) particulate matter CBSFC (g/hp · hr) (g/hp · hr) (g/hp · hr) (g/hp · hr) (lb/hp · hr) EPA-1 0.87 2.4 12.7 0.37 0.464 EPA-2 0.80 2.2 12.9 0.42 0.474 EPA-3 0.78 2.1 12.9 0.36 0.460 Mean 0.82 2.2 12.8 0.38 0.466 c.o.v. 6% 7% 1% 8% 2% Cal-1 0.78 1.8 12.7 0.34 0.467 Cal-2 0.77 1.9 12.3 0.35 0.457 Cal-3 0.72 1.6 12.7 0.32 0.466 Mean 0.76 1.8 12.5 0.34 0.463 c.o.v. 4% 6% 2% 5% 1% B20-1 0.78 2.2 13.4 0.36 0.462 B20-2 0.73 2.0 13.4 0.38 0.468 B20-3 0.82 1.9 13.8 0.38 0.470 Mean 0.78 2.0 13.5 0.37 0.467 c.o.v. 6% 9% 2% 3% 1% C20-1 0.75 1.9 13.1 0.36 0.468 C20-2 0.80 1.8 13.3 0.39 0.473 C20-3 0.73 1.8 13.1 0.37 0.467 Mean 0.76 1.8 13.1 0.37 0.469 c.o.v. 11%  3% 2% 5% 1%

These data indicate that B20 diesel blend results in increased NO_(x) emissions in both line-haul and switch duty cycles and increased exhaust opacity (represented by emission of particulate matter) in line-haul duty cycle conditions. (With respect to particulate matter, the 2004 study concluded that the type of fuel utilized had little impact on the amount of particulates emitted because such emissions in two-cycle diesel engines are dominated by lubricating oil-generated components.) The testing summarized in Table 2 appears to show that this is not necessarily true with respect to the present fuel composition.

Each of the emissions characteristics of the present fuel composition is highly desirable, both individually and in combination. This is particularly true in view of the fact that railroad engine emissions are coming under scrutiny from environmental agencies such as the EPA. Because two-cycle diesel engines constitute the vast majority of engines in use on railroads throughout North America and because off-road #2 petrodiesel generally is considered a relatively dirty fuel (i.e., its combustion results in large amounts of particulates, SO₂, NO_(x) species, etc.), the availability of alternative fuels that can assist these engines in meeting more stringent emission standards is highly desirable.

While the present fuel composition has been found to provide significant emission benefits when used in two-cycle diesel engines, similar levels of improvement have not yet been proven in the four-cycle diesel engines more commonly employed in automobiles such as longhaul trucks; more accurately, initial, cursory studies do not appear to indicate that the improvements are as dramatic as those seen in two-cycle diesel engines. This could be due to any one or more of a variety of factors including pressure and temperature differences in the respective combustion chambers, more efficient cooling of combustion chambers in four-cycle engines, and the like.

However, the aforementioned cursory studies have shown other advantages in the use of a fuel composition according to the present invention. For example, tests on a four-cycle Cummins™ turbo, inter-cooled diesel engine (set up to run at 2200 rpm, which was believed to fairly approximate a freight truck at a constant velocity of 24.6 m/s, i.e., 55 mph) using a commercially available #2 petrodiesel (A) and three alternative fuels—a commercially available B20 biofuel (B), i.e., an 80:20 blend of petrodiesel and a methyl ester derivative of soybean oil, filtered waste vegetable oil (C), and a fuel composition according to the present invention (D)—resulted in the following engine efficiency data:

TABLE 5 Engine Efficiency, Four-Cycle Diesel Engine A B C D Engine efficiency* (%) 100 98.6 90.3 99.1 Coolant temp. increase (° C.) 25 26 28 23 Fuel efficiency (km/L) 10.6 10.3 8.5 9.3 *Relative to petrodiesel. The engine efficiency on each fuel was calculated using the formula η_(e)=1/(BFSC×LHV) where η_(e) is the engine efficiency for a given time interval, BFSC is the brake specific fuel consumption for that time interval, and LHV is the lower heating value of the fuel. The coolant temperature increase was determined after the engine had been warmed as close as possible to 71° C. (160° F.) before running it for 15 minutes with each fuel type.

Based on the data of Table 3, a fuel composition of the present invention appears to result in a calculated engine efficiency that is far better than that of waste vegetable oil and even better than that of a commercial B20 diesel blend. Also, use of a fuel composition according to the present invention resulted in a coolant temperature increase less than that of all other fuels tested, including two commercial fuels. With respect to fuel efficiency, a fuel composition of the present invention exhibited 10% better results than a fuel made from waste vegetable oil; additionally, assuming a linear extrapolation of efficiency decrease with an increase in percentage of biofuel in the blended product, the same fuel composition appears to yield ˜5% better results than a biofuel presently considered commercially acceptable, i.e., a methyl ester derivative of soybean oil. This is contrary to reports of better power and consumption results for methyl esters relative to equivalent ethyl esters; see, e.g., the Peterson et al. article and publications cited therein (all of which compare “pure” biofuels, i.e., biofuels not containing significant amounts of free alcohol).

At least the last of the foregoing efficiency results is somewhat surprising in view of the fact that the present fuel composition includes a not significant amount of an alcohol such as ethanol. The presence of such alcohols in a petroleum-based fuel typically would be expected to yield reduced fuel efficiency values. However, the foregoing results seem to indicate that the present fuel composition provides better fuel efficiency than “pure” biodiesel products.

Use of the present fuel composition does not appear to require the use of any special equipment or to require the modification of existing engine equipment. Specifically, some literature and manufacturer warranty information appears to indicate that special seals and gaskets are required if a neat biofuel is to be run in an engine. However, none of the testing to date has shown this to be necessary with the fuel composition of the present invention.

Conversely, use of the present fuel composition has been shown to have at least one positive effect on equipment in which it is used. Specifically, combustion of the composition fuel appears to provide a detergency effect to metal engine parts. Contrary to other studies (see, e.g., the Peterson et al. article) which have seen either no improvement in coking or even somewhat worse coking, use of the present fuel composition in a two-cycle railroad diesel engine has resulted in metal parts (e.g., fuel injectors and cylinders) that are far cleaner than before they were prior to use of the present fuel composition.

At present, this effect is not fully understood. Specifically, whether the fuel composition actually provides a detergency effect that helps to remove previous deposits or whether the fuel composition merely reduces the amount of new deposits to a level that permits normal operation of the engine to remove prior deposits (e.g., through vibrations) is not known. However, what can be said with some certainty is that engine parts that are coated with fewer deposits are expected to be easier to cool and to run more efficiently.

Terms and phrases used in this description are believed to assist in the understanding of the composition and processes of the present invention. However, no unnecessary limitations are to be implied from the brief, concise description of illustrative embodiments provided. 

1. A fuel composition comprising: a) at least about 2.5% (by vol.) of at least one C₂-C₆ alcohol, and b) at least one C₂-C₆ ester of one or more long chain fatty acids, wherein at least one of the following is true: (1) said fuel composition exhibits a pH of less than about 6.8, and (2) said fuel composition has a kinematic viscosity of less than about 4.0 centistokes.
 2. The fuel composition of claim 1 wherein said composition exhibits a pH of less than about 6.8 and has a kinematic viscosity of less than about 4.2 centistokes.
 3. The fuel composition of claim 1 wherein said composition exhibits a pH of from about 5.5 to about 6.7.
 4. The fuel composition of claim 3 wherein said has a kinematic viscosity of less than about 4.2 centistokes.
 5. The fuel composition of claim 1 wherein said composition comprises at least about 0.2% (by vol.) water.
 6. The fuel composition of claim 1 wherein said composition has a cloud point of at least as low as −5° C. when measured in accordance with ASTM D2500.
 7. A fuel composition comprising: a) from about 5 to about 10% (by vol.) of at least one C₂-C₆ alcohol, and b) at least one C₂-C₆ ester of one or more long chain fatty acids, said fuel composition having a kinematic viscosity of from about 3.5 to about 4.0 centistokes.
 8. The fuel composition of claim 7 wherein said composition exhibits a pH of from about 6.0 to about 6.7.
 9. The fuel composition of claim 7 wherein said composition is essentially free of at least one of sulfur and nitrogen atoms.
 10. The fuel composition of claim 7 wherein said composition comprises at least about 0.2% (by vol.) water.
 11. The fuel composition of claim 7 wherein said composition has a cloud point of at least as low as −5° C. when measured in accordance with ASTM D2500.
 12. A process for providing a fuel composition, comprising: a) providing a liquid that contains at least one C₂-C₆ ester of one or more long chain fatty acids, b) adjusting the pH of said liquid to less than 7.0, thereby providing a raw fuel composition, and c) optionally, treating said raw fuel composition so as to remove particulates having an average diameter greater than about 1 μm, thereby providing a refined fuel composition.
 13. The process of claim 12 wherein said at least one C₂-C₆ ester is provided by transesterifying a triglyceride-containing composition using a C₂-C₆ monool.
 14. The process of claim 13 wherein said C₂-C₆ monool comprises ethanol, said ethanol optionally being present in stoichiometric excess.
 15. The process of claim 12 wherein said fuel composition comprises at least about 0.2% (by vol.) water.
 16. The process of claim 12 wherein said fuel composition comprises less than about 5 parts per million of Group I metal ions. 17-20. (canceled) 